Glucose infused through the portal vein enhances liver gluconeogenesis and glycogenesis from [3-14C]pyruvate in the starved rat

After a pulse of [3-14C]pyruvate, 24 hr starved rats were infused through the portal vein with two different doses of glucose (7.8 or 20.8 mg/min) or the medium, and blood was collected from the inferior cava vein at the level of the suprahepatic veins. The highest dose of glucose enhanced the appearance of [14C]glucose in blood from the 2nd to the 20th min after tracer delivery. It also enhanced production of [14C]glycogen and concentration of glycogen in the liver after 5 and 20 min. At 20 min of glucose infusion the appearance of [14C]glyceride glycerol in liver as well as liver lactate concentration and lactate/pyruvate ratio were increased. The low dose of glucose used enhanced liver values of [14C]glycogen, [14C]glycogen specific activity and glycogen concentration. Our results support the hypothesis that in the starved rat glucose is converted into C3 units prior to being deposited as liver glycogen and based on the liver zonation model (Jungermann et al., 1983) it is proposed that glucose stimulated gluconeogenesis by shifting the liver to the cytosolic redox state as a secondary consequence of increased glycolytic activity.     

Postischemic Cerebral Lipid Peroxidation In Vitro: Modification by Dietary Vitamin E

Using an in vitro system, we studied the effect of postischemic reoxygenation on cerebral lipid peroxidation in relation to the dietary intake of vitamin E (VE) in rats. Homogenates prepared from VE-deficient, -normal, and -supplemented brains, which were previously rendered ischemic for 30 min by decapitation, were incubated under air or nitrogen gas for 60 min. The extent of peroxidation in brain tissue was estimated by a thiobarbituric acid (TBA) test and by diene conjugation in total lipid extracts. The brain levels of alpha-tocopherol and of total and free fatty acids (FAs) were also determined. Aerobic incubation increased TBA reactants in all dietary groups; the effect was largest in the VE-deficient group, intermediate in the VE-normal group, and smallest in the VE-supplemented group. In contrast, nitrogen incubation did not alter the basal levels of TBA reactants except for a small rise associated with VE deficiency. Conjugated dienes changed in parallel with TBA reactants. alpha-Tocopherol decreased after aerobic incubation and also, to a lesser degree, after nitrogen incubation in each dietary group. Only in the reoxygenated samples of the VE-deficient group was there a significant fall in total polyunsaturated FAs. The levels of free FAs continuously increased throughout ischemia and subsequent incubation. However, the level of free polyunsaturated FAs was similar after aerobic and nitrogen incubation in each dietary group, and was not affected by VE. Thus, cerebral reoxygenation after ischemia propagates peroxidative reactions within esterified polyunsaturated FAs. The modification by VE of reoxygenation-induced lipid peroxidation suggests free radical mediation.     

Mechanism of inhibition by lithium of sodium transport in the toad bladder

Lithium transport across the urinary bladder of Bufo marinus has been studied by means of the short-circuit current technique, as well as unidirectional ion flux measurements. Exposure to lithium of the epithelial (mucosal) surface of this preparation led to a slow, progressive decrease of ion transport, with increasing discrepancy between short-circuit current and lithium influx; in fact there was still an appreciable lithium influx across bladder exposed to amiloride even though short-circuit current was suppressed. Ohmic conductance and sodium efflux barely increased under these circumstances. Upon replacement of lithium by sodium on the epithelial side, the preparations recovered slowly indeed, and residual lithium could be detected in bladder tissue for more than 2 hr while the rate of sodium extrusion at the basal-lateral cell border was slowed down. Recovery from exposure to lithium was accelerated by vasopressin and amphotericin, both of which facilitate sodium entry at the apical border of the epithelium. Thus the lasting deleterious influence of lithium on sodium transport might result from the fact that this ion, once trapped in the cytoplasm, closes the sodium channels.     

Detection of an antigenic cell wall layer inHistoplasma capsulatum

Histoplasma capsulatum yeast cells have been studied by immunoelectron microscopy using rabbit polyclonal antisera and a biotin-avidin-peroxidase detection system. An antigenic surface layer has been visualized in the cell wall of immunostained organisms. This layer was not seen in samples prepared by standard electron microscopic methods or in negative controls used with the immunocytochemical technique. Without immunostaining the cell wall ofHistoplasma appeared almost transparent. In contrast, after immunoperoxidase staining the cell wall was conspicuous, bounded by the darkly stained outer layer. This electron dense layer, appeared to be a reservoir of surface antigens that were recognized by anti-Histoplasma antibodies.Abbreviations CHHA Cystine-heart-hemoglobin agar - PBS phosphate buffered saline - Ig immunoglobulin - TBS Tris buffered saline - DAB 3,3-diaminobenzidine tetrachloride - FITC fluorescein isothiocyanate - M199 tissue culture medium 199, according to Morgan et al. (1950)     

Root growth and litter decomposition in a coffee plantation under shade trees

In a non-fertilized coffee plantation under shade trees the root biomass was excavated to estimate its distribution in the soil profile. One third of total fine (less than 1 mm) roots was found in the first 10 cm of soil; the cumulative total to 30 cm reached 73%. A highly variable and transient amount of fine roots colonized the litter layer. Root production both in the litter and in the first 7.5 cm of mineral soil was estimated from sequential samplings and was 10 g m^–2 yr^–1 and 660 g m^–2 yr^–1 respectively. The decomposition rate of weighed averages of litter fractions in the coffee plantation, calculated as the ratio of litter fall rate to the amount found in the soil was k=4.8. Shade tree leaves, the major component of litter descomposed slower than coffee leaves and these slower than flowers and fruits. Litter bag experiments showed considerable slower rates when mesh was 0.03 mm than 0.5 mm. Nitrogen and phosphorous showed increases in concentrations as decomposition progressed while potassium, calcium and magnesium followed a decrease in concentration that paralleled that of dry weight loss. In comparing the decomposition rate for litter with or without coffee roots growing in the bags, a tendency to show faster decomposition rates was found for the treatment with roots. These differences were however, only significant for one month for shade tree leaves litter. Nitrogen amounts remaining in shade tree leaves litter was lower in the treatment with roots that without roots. Potassium concentration in roots was positively correlated with potassium concentration in decomposing leaf litter where roots were growing. These results suggest that while roots growing attached to decomposing litter had little or no effect in speeding the decomposition process, the superficial roots seem to play an important role in absorbing very efficiently the mineralized nutrients from litter. The anatomical study of roots showed that the plantation is intensely infected with V-A mycorrhiza. External mycorrhizal hyphae did not to play a role in attachment of roots to decomposing litter while root hairs were found to grow in profusion on root surfaces oriented toward litter.     

Changes with starvation in the rat of the lipoprotein lipase activity and hydrolysis of triacylglycerols from triacylglycerol-rich lipoproteins in adipose tissue preparations.

Lipoprotein lipase activity was higher in fat-pad pieces than in isolated adipocytes from the same fed rats, whereas hydrolysis of triacylglycerols from triacylglycerol-rich lipoproteins was similar in the two preparations when incubated either in basal conditions or in the presence of heparin. In both preparations there was a similar release of lipoprotein lipase activity into the medium during basal incubation, enhanced by the presence of heparin. In fat-pad pieces, but not in isolated adipocytes, incubation with heparin produced a decrease in the lipoprotein lipase activity measured in the tissue preparation. In fat-pad pieces from 24 h-starved rats, lipoprotein lipase activity was the same as in isolated adipocytes from the same animals and incubation with heparin did not affect the appearance of lipoprotein lipase in the medium or the utilization of triacylglycerols from triacylglycerol-rich lipoproteins. These results support the following conclusions. (1) The effectiveness of lipoprotein lipase in adipose tissue preparations in vitro depends more on its availability to the substrate than on its total activity. (2) Heparin acts on adipose tissue preparations from fed animals both by enhancing the release of pre-existing extracellular enzyme (which is absent in isolated adipocytes) and by enhancing the transfer outside the cells of the intracellular (and mainly undetectable) enzyme that is activated in the secretion process. (3) In adipose tissue from starved animals there is not only a decrease in the active extracellular form of lipoprotein lipase activity but also a reduction in the intracellular (and mainly undetectable) pool of the enzyme.     

Role of molybdenum in nitrate reduction by chlorella

Molybdenum is absolutely required for the nitrate-reducing activity of the nicotinamide adenine dinucleotide nitrate reductase complex isolated from Chlorella fusca. The whole enzyme nicotinamide adenine dinucleotide nitrate reductase is formed by cells grown in the absence of added molybdate, but only its first activity (nicotinamide adenine dinucleotide diaphorase) is functional. The second activity of the complex, which subsequently participates also in the enzymatic transfer of electrons from nicotinamide adenine dinucleotide to nitrate (FNH₂-nitrate reductase), depends on the presence of molybdenum. Neither molybdate nor nitrate is required for nitrate reductase synthesis de novo, but ammonia acts as a nutritional repressor of the complete enzyme complex. Under conditions which exclude de novo synthesis of nitrate reductase, the addition of molybdate to molybdenum-deficient cells clearly increases the activity level of this enzyme, thus suggesting in vivo incorporation of the trace metal into the pre-existing inactive apoenzyme.     

Lethal and Mutagenic Action of Black Light (325 to 400 nm) on Haemophilus influenzae in the Presence of Air

Near-ultraviolet (UV) light (325 to 400 nm), in the presence of air and the absence of exogenous photosensitizing compounds, is lethal and mutagenic for Haemophilus influenzae. The lethal effect is the same for both wild type and streptomycin-resistant mutants, indicating that the mutants are not selected by the irradiation. The inactivation and mutagenicity show a large shoulder, suggesting the existence of repair systems. Filters were used to eliminate the possibility of short-UV irradiation. The effective radiation is between 325 to 400 nm. The lethal and mutagenic effects are higher during mid and late log phase than during early log or stationary phase.     

A strain of Holmes' ribgrass virus occurring in Yugoslavia

A virus having 300 nm long rod-shaped particles was isolated fromPlantago media L. in Yugoslavia. The virus was transmitted to 15 species of host plants the symptoms of which are described in detail. The symptoms corresponded to those that appeared after infection by the original Holmes' ribgrass virus (HRV). The investigated virus was compared both with the common strain of tobacco mosaic and the original Holmes' ribgrass viruses by means of serological tests. The agar double-diffusion tests showed that it is closely related to HRV and remotely related to the common strain of TMV. On the basis of these results we concluded that this virus represented a strain of the HRV. The investigations of the cell inclusions showed that our virus produced rounded plates instead of hexagonal prisms. Electron micrographs of ultrathin sectioned material demonstrated that these plates were formed by virus particles lying perpendicularly to the layers of the plates. The presence of plates also points to the fact that the investigated virus belongs to the HRV.     

Micromorphology of Cryptococcus neoformans

Fine details of the internal and external morphology of Cryptococcus neoformans as seen in ultrathin sections are described and illustrated with electron micrographs. The capsule characteristic of this species contained microfibrils (30 to 40 A in diameter) that appeared to radiate from the cell wall and to coil and intertwine in various directions. These thin, uniformly structured, electron-dense filaments are believed to represent complex polysaccharide molecules. The internal morphology of C. neoformans was in many ways similar to that of yeasts studied by other authors. The cell was uninucleate with a single nucleolus. The nuclear envelope, a pair of unit membranes interrupted by pores, was typical of that found in eucaryotic organisms. Smooth endoplasmic reticulum, mitochondria, vacuoles, storage granules, and ribosomes were consistent features of the cytoplasm. In addition, C. neoformans presented membranous organelles derived from the plasma membrane and comparable to bacterial mesosomes and mitochondria of an annulate type.